Postal

Postal is a self-hosted mail server designed as an open-source alternative to SendGrid or Mailgun. Handles outbound and inbound, RESTful API, multi-domain. Operationally heavier than just running Postfix.

An agent stack treats email as a two-way primitive. Inbound has to arrive as structured JSON a tool call can consume, sends have to be safe to retry when a model loop repeats itself, and every action needs an audit trail. A provider without inbound parsing only solves half the problem.

Against inbound parsing into tool calls and model-generated sends that must not duplicate, Postal covers inbound parsing, webhook coverage, event stream, batch sending, SDK breadth, and multi-tenant support, and does not cover idempotency keys. Whether that gap matters depends on how central those are to the build.

• Inbound parsing: Yes
• Idempotency keys: No
• Webhooks: Yes
• Operating since: Not published
• Event stream: Yes
• Best published rate per 1,000: Tiers not published in comparable form
• Batch sending: Yes
• SDKs: node, ruby, php
• Multi-tenant: Yes

You own it. Reputation depends on your IP, warmup discipline, and authentication.

Teams with infra ops capacity that want full control of their mail delivery.